The Greens are calling on Treasurer Scott Morrison to pull out of a planned address at the upcoming Australian Christian Lobby conference.
Morrison will be speaking at the event to be held in Sydney on Saturday, April 23, alongside Christian author Eric Metaxas, conservative News Corp columnist Miranda Devine and Indigenous leader Noel Pearson.
But Greens LGBT spokesman Robert Simms says the ACL is simply a hate group which should not be validated by the Treasurer.
"The Liberals need to stop legitimising these hate merchants. The ACL are an extreme organisation. Why on earth the federal Treasurer would be wanting to legitimise their political approach is beyond me," he said.
Simms also called on prime minister Malcolm Turnbull to stand up to the conservative forces within his own party.
"When it comes to Malcolm Turnbull, actions speak louder than words. Even though he talks about offering a different direction to Tony Abbott, he's been found to be severely wanting."
A spokesman for the Treasurer defended his decision to address the group, pointing out that opposition leader Bill Shorten spoke at the same event in 2014.
"There is a long tradition of political leaders of both sides of politics attending and speaking at ACL events," the spokesman said. "The Treasurer's attendance will be confined to providing an address to the ACL, just as Bill Shorten did in 2014."
But it's unlikely Morrison, who is a committed Christian, will take the same attitude into his speech that Shorten took to his in 2014.
Shorten used his address to the group to condemn its opposition to marriage equality, saying the group used the bible to attack "blended families", like his.
"When I see people hiding behind the bible to insult and demonise people based on who they love…I cannot stay silent. I do not agree," he said.
"When I hear people allege that 'God tells them' that marriage equality is the first step on the road to polygamy and bigamy and bestiality…I cannot stay silent. I do not agree."
"These prejudices do not reflect the Christian values I believe in."
The ACL has a history of making controversial comments on LGBT issues.
A petition has now been started, demanding Morrison pull out of the event.
"For years the Australian Christian Lobby have actively attacked the rights of LGBTI people by campaigning against almost every legislative reform designed to treat LGBTI people as equal citizens," it reads.
"No member of Parliament should be involving themselves with an organisation that seeks to harm members of our community, and no member of Parliament should be speaking at this conference."
This year's conference is running under the theme, "Cultivating Courage", and is billed as an opportunity for Aussie christians to come together as a "voice for values."
"There's no doubt it is becoming harder to be a Christian in Australia. Elite opinion mocks faith," the event's website reads. "[However] we can draw courage from the role Christianity has played in shaping our own history, and the opportunities that lie before us for a courageous church to continue to impact our culture."
Other previous speakers at ACL events include former prime ministers John Howard, Kevin Rudd and Tony Abbott, as well as former Treasurers Peter Costello and Wayne Swan and NSW Premier Mike Baird.